Making room for DDR DIMMs

STMicroelectronics is now shipping a chip-level 10-resistor network called the DDR110-xxT7 that is intended to make life easier for designers who want to take advantage of 266 MHz double data-rate (DDR) synchronous DRAMs mounted on dual in-line memory modules (DIMMs). (Yes, we know that you are hip to the acronyms, but it's always good to spell them out on occasion for newbies.) DDR DIMMs use series stub terminated logic (SSTL), which requires a parallel termination resistor on each line. Besides saving motherboard space by eliminating termination cards, the DDR110-xxT7 automatically disconnects its termination resistors when you use single data-rate (SDR) DIMMs. The DDR110-xxT7 works with PC100, PC133, PC1600, and PC2100 DIMMs, and also works as a companion device for the Aladdin Pro 5 and ALiMAGiK1 system chip sets from ACER Labs, the SIS635 and SIS735 from SIS, and the Apollo PRO266 and Apollo KT266 from VIA. To handle both DDR and SDR DIMMs, each of the DDR110-xxT7's 10 termination resistors has a switch. The switches are controlled in unison by the chip's TTL-compatible Output Enable (OE) signal line, which connects the resistors from input to output - typically a 1.25V termination voltage - when set high, and disconnects them, leaving an open circuit, when set low.